Integrated circuit devices, each of which contain a plurality of logic circuits (inverters, gates, flip-flops, etc.) composed of semi-conductor elements (resistors, diodes, transistors, etc.) are tested for early life failures prior to their end use in particular circuit applications. Such a test typically comprises a burn-in process wherein devices are subjected to required test parameters for a period of time often in an austere environment such as in an elevated temperature chamber. The test progress is constantly monitored and the results recorded. A device under test is usually discarded whenever any semi-conductor element on it fails.
Since the required burn-in test period is typically two or more hours and the test facilities expensive, it is expedient that a large number of devices be tested at the same time by the same facility. Normally, each individual device has its input and output leads individually connected to the test set independently of all other devices; and only the power and ground connections are common or shared among all devices. Test signals are introduced on the individual input leads and the output signals on the output leads are monitored to determine if these signals deviate from predetermined ranges of values which deviant signals indicate a malfunctioning device.
Since integrated circuits have a plurality of input and output leads, a small test facility testing 1000 integrated circuits could require in excess of 12,000 wires interconnected between the devices under test and the facility. As is readily apparent, the large number of required test connections severely limit the number of devices which can be physically located in a test unit while also requiring excess operator time in setting up the test apparatus and add to the chances that an improper test connection may be made thereby causing invalid test data.
Multiplex equipment is also required in most test facilities since the test facility is unable to simultaneously monitor response signals appearing on the output leads for all 1000 circuits under test at the same time. The multiplex equipment switches connecting between the test facility and groups of the 1000 circuits, say fifty circuits at a time, in a preselected sequence to test the 1000 circuits fifty at a time.
There is, therefore, a need for a test method and apparatus for testing a plurality of electrical devices without the need for a large number of electrical interconnections and associated multiplex equipment between the devices and the test apparatus.